Don't ever click on a link who somebody has sended to you because it could be infected and always check your urls before opening them. Invest in coins where you know that you can get at least a little bit back.
Not on ICO's where you can see that its nice but it needs support sometimes.
Very important information that do not join any airdrop if you are not convinced with the ide or found anything suspicious. Also if anyone send any link for the airdrop just do not open it. Also if you are sure about some good ICO, then invest at early stages so that you can get the coins at good discounted rate.